Particularly as a result of the high and still increasing numbers of electric motors produced and despite their traditional basic structure with a basic body of an insulating material, preferably a duroplastic material, and with metallic lamellae at the periphery (cylindrical collector) or at a front side (plane collector), collectors have underdgone extensive development, affecting various details. This development was intended to take into account the function of the collectors, their simple and reliable installation, their robustness and long service life and, last but not least, low production costs.
A collector is subjected to particularly high stresses during the installation, for which the connection of the winding conductors to the lamellae and, even more so, the pressing of such a collector onto the shaft of a motor are critical. In the past, the latter has led to critical stresses in the case of collectors with a uniform basic body consisting of a duroplastic insulating material. These stresses were dangerous even when they produced only invisible, internal destruction or cracks.
Typically, forces of several thousand Newton are employed to mount a collector on the shaft of an electric motor. For this reason, a sheathing has long been used, so that the seat of the collector towards the shaft is formed by an internal metallic bushing, which is capable of absorbing the much higher expansion forces and frictional forces encountered when mounting a collector on a shaft, than is the insulating material. Because of the high load-carrying capability and stiffness of the metal, such a bushing element is in a position to keep the insulating effectively free of the high shear and tensile stresses that develop as the collector is pressed onto the shaft of the motor. After that, the bushing can keep the tensile stresses emanating permanently from the press fit away from the insulating material.
Such a busing element presupposes, however, a production process, which is capable of complying with close tolerances. Typically, the bushing element, after it has been pressed together with the lamellae with the insulating material to an integral basic body, must be finished, in order to compensate for adjustment errors that arise during the installation and the pressing. Such finishing work on cast metal bushing elements is costly.
Accordingly, there have also already been attempts to embed a spiral spring element, rather than a metallic bushing element, at the inside of the borehole in the basic body of insulating material. Because of its elasticity, this spiral spring element can be put easily and flush on a mandrel in the injection mold for the basic body of insulating material. However, such a spring element is only conditionally adequate to absorb the forces that develop when a collector is pressed and seated onto the shaft of the motor, because it is deformable in the axial direction and because the spreading forces emanating from the press fit can pass through the windings.